Typically either a drum brake or a disc brake is provided to halt rotation of the motor in traction elevators. In either case, at least one compression spring is generally employed to bias the brake into its closed or braking position and an actuator which is typically electromagnetically, hydraulically or pneumatically driven is provided to overcome the spring bias and move the brake into its open or released position permitting the motor to commence rotation and thereby raise or lower an elevator car along a hoistway. These brakes are regarded as fail-safe systems since if, for example, power is lost to the actuator, the brakes under the influence of the biasing springs automatically assume the braking or closed position.
In such circumstances it is often necessary to evacuate any passengers entrapped within the elevator car. U.S. Pat. No. 6,273,216 B1 describes an emergency release device that enables remote manual release or opening of an electromagnetic elevator drive brake and subsequent manual movement of the elevator car to the next floor of the building by way of the elevator drive. The device is accommodated within a niche positioned alongside the elevator hoistway at a convenient location within the building, such as a landing floor, to enable easy access by service technicians. It includes a handle, typically in the form of bicycle brake lever, together with a rotatable handcrank. On drawing of the handle force is imparted, by way of a cable, to a brake release linkage arranged remotely at the brake of the elevator drive. Through the rotation of the handcrank the elevator motor can likewise be rotated by way of a crown wheel gear transmission, and thus the elevator car can be moved in the desired direction to evacuate any passengers at the nearest landing.
An alternative arrangement is disclosed in GB 2 407 554 A whereby a piston and cylinder arrangement is mounted to actuate the brake release linkage. When evacuation is required a piston pump such as a foot pump or lever operated hand pump is repeatedly operated with intermittent flow to build up pressure in the piston and cylinder arrangement and move the brake release linkage and open the electromagnetic brake. Thereby the elevator car can move slowly in small stages to permit evacuation without activating the car-mounted safety gear.
Generally, it is more practical and economical to use hydraulic elevator drive brakes rather than electromagnetic brakes to provide the necessary, relatively large braking forces associated with drives used in high torque applications such as high-rise or high speed elevator installations. In such instances, it may not be possible to use the manually operated mechanical linkage release mechanisms described above to achieve the forces required to release the hydraulic drive brake. This problem is further compounded by the requirement in the elevator industry to provide redundant braking on all elevator drives accordingly increasing not only the force but also the complexity of the linkage system required to open multiple brakes simultaneously.
If power is lost in a hydraulic braking system, valves within the hydraulic actuator automatically direct or drain fluid from the brake pistons to a reservoir. Accordingly, there is no pressure counteracting the compression spring within the brakes and the brakes assumes their closed or braking position. It has been previously proposed to use a piston pump, such disclosed in GB 2 407 554 A, in an evacuation situation to directly connect to the hydraulic system to build up pressure to overcome the spring bias within hydraulic brakes and thereby release the brakes. However the operator not only has to manually and repeatedly operate the piston pump but must simultaneously manipulate the valves to prevent the hydraulic fluid from draining directly back to the reservoir. This is a difficult if not impossible task and the operator is prone to mechanically jam the valves in their closed position. However such a situation can lead to the brakes remaining uncontrollably open and may lead to accidents. Furthermore, while the intermittent flow from piston pumps is extremely effective at gradually lowering or raising the elevator car to evacuate any passengers at the nearest landing, these systems cannot be used during commissioning for example when it is necessary to keep the brake released for prolonged periods to test the effectiveness of car-mounted safety gears.